Presently we do not know how and why this training is so effective. However, there are many theories and Dr. Berard had some himself. Below are listed some of the most common theories but first let’s review some basic anatomy so you will be able to better understand them.
A Brief Overview of the Ear:
The middle ear contains the body’s three smallest bones (malleus, incus, and stapes; together they are termed the ossicles,) and two of the body’s smallest muscles (tensor tympani muscle and stapedius muscle.) When sound enter the outer ear and strikes the tympanic membrane (i.e., the eardrum,) the vibration of the eardrum causes the malleus to move, which in turn moves the incus, which moves the stapes. The vibrating stapes then strikes the oval window of the inner ear (cochlea,) which then causes fluid on the cochlea to bend the tiny hair cells which the auditory nerve then interprets as various sounds.
The tensor tympani muscle and the stapedius muscle are responsible for providing the proper tension to the ossicles. Additionally, when exposed to a loud sound, the two muscles react together, which in turn restricts the movement of the ossicles. As a result, the stapes strikes against the inner ear with limited force. This is known as the acoustic reflex. This is important in protecting the person from loud and harmful sounds which could injure the auditory nerve.
Theories Related to the Middle/Inner Ear
“Reduction in peaks is due to a decrease in stimulation”! (filtering) - Guy Berard, MD. During the AIT listening sessions, filters are used to dampen those frequencies which the person hears too well. Dr. Berard theorized that filtering will reduce sensitivity due to the lack of stimulation to certain area of the cochlea and/or the brain during the listening experience. Furthermore, those area(s) of the cochlea and/or brain which are not filtered, receive intense stimulation.
Thus, the peak frequencies are slightly reduced because of a lack of stimulation, and the non-peak frequencies are slightly improved because of stimulation. The end result is an improvement and balance in hearing, and a relatively straight line on the audiogram.
Biochemical Changes There are theories related to biochemical changes in the brain, especially opioid activity and melanin.
Opioid Hypothesis – Jack Panksepp. The beta-endorphin hypotheses of AIT suggests that the modulated music stimulates, and possibly normalizes, certain areas of the brain which release endogenous opioids. It is established that listening to music activates endogenous opioids. One possible area in the brain involved in the release of beta-endorphins is the inferior colliculus of the midbrain, which receives sound input and is rich in opioid receptors. For more information related to this theory refer to: Autism Research Review International, 1995, Vol. 9 (4)
Melanin Hypothesis – Lisa Boswell. Boswell speculates that AIT reduces sound sensitivity and improves pineal function by increasing melanin in the stria vascularis in the middle ear. The stria is the “battery” of the cochlea. Additional melanin in the stria would result in changes in the endolymph and hair cell function. Melanin has many functions, from aiding neural development to increasing neural transmission. Melanin in the inner ear can absorb acoustic energy much as melanin in the skin absorbs photic energy. Research has demonstrated increased strial melanin in response to impulse noise. Increased melanin through AIT might help normalize audiograms and mitigate the effects of hyperacusis on the pineal gland, which responds to environmental stimuli. AIT could then improve pineal function, normalize circadian rhythms, and decrease autoimmune symptoms. This would explain why Dr. Berard noted improvements in allergic disorders such as eczema, hay fever, and asthmas after AIT.